1. Field of the Invention
The present invention relates generally to a medical prostheses and more particularly to a variable cohesive gel, form stabilizing, implant which may be used for augmentation or reconstruction of the breast. The implant may be a mammary prosthesis or a soft tissue expander.
2. Discussion of the Related Art
Today, augmentation or reconstruction of the breast requiring an implantable medical prosthesis has become fairly common practice in the art of plastic and reconstructive surgery. Typical permanent prostheses, which are often selected for these procedures, include round silicone shells, or envelopes, pre-filled with silicone gel or filled at the time of surgery with normal saline solution.
In recent years, the prostheses used for these procedures have raised cause for concern with respect to maintaining breast shape after surgical implantation. During post-operative follow-up—once healing has progressed—surgeons often observe undesirable alterations in the patient's breast shape, specifically signs of skin and/or soft tissue deformation, commonly known to those skilled in the art as prosthesis wrinkling, knuckling or scalloping. These adverse effects usually occur at the upper or lower pole of the prostheses, along the perimeter of the prosthesis shell or at the base, i.e. the inferior portion closest to the inframammary fold, and become more evident when the recipient changes her anatomical position. Moreover, with the patient in an upright position, these unstable prostheses have been known to collapse or fold in the upper pole and knuckle in the lower pole, further increasing risk of deformed breast shape. Medical prostheses have been proposed in an attempt to eliminate these clinical problems, but adverse alterations in breast shape continue to exist.
As described in U.S. Pat. No. 6,605,116, implantable mammary prostheses generally have a relatively flat posterior face that is placed against the patient's chest and a domed anterior face that projects outward. It is often desirable for the perimeter region, where the anterior face meets the posterior face, to have a relatively small radius of curvature, particularly at the upper pole or superior portion of the prosthesis, i.e., the portion of the prosthesis that is uppermost when the patient is standing. A relatively narrow radius of curvature in the transition between the anterior face and the posterior face in the upper pole of the prosthesis is desirable because it permits a relatively smooth transition between the mammary tissue and the implant when the prosthesis is implanted. But a small radius is sometimes associated with the appearance of creases that extend inward from the perimeter of the prosthesis in the region of relatively small radius. This is sometimes referred to as a scalloping effect. Scalloping tends to occur when the prosthesis is filled with fluid or gel and the patient is upright such that the weight of the filling material is pulling downward on the prosthesis. The creases often appear on the anterior face and around the perimeter of the prosthesis. This is aesthetically undesirable as the creases can sometimes be discerned through the overlying skin of the patient.
U.S. Pat. No. 5,480,430 relates to a fluid-filled breast prosthesis for surgical implantation beneath the skin having a wrinkle resistant, elastic outer shell that is adapted to resist deformation or wrinkling during movement of the fluid filler. The outer shell, or envelope, has superior and inferior portions. The wall of the superior portion of the shell is substantially thickened with respect to the wall thickness of the inferior portion of the shell. The shell forms an envelope with an inner cavity, which is filled with a biocompatible liquid such as saline. The presence of the thickened superior portion of the shell prevents wrinkles from forming in the breast prosthesis during fluid displacement, such as when the breast prosthesis recipient changes her anatomical position. The differentially thickened shell has a posterior base portion, which may be reinforced to further stabilize the prosthesis.
U.S. Patent Application No. US 2002/0143396 A1 (U.S. Pat. No. 6,605,116) relates to reinforced radius mammary prostheses and soft tissue expanders. The prosthesis is configured such that the average thickness of the shell in the region where the posterior and anterior faces meet is greater, e.g., at least twice the average thickness of the shell in the region of the anterior face. The inventors suggest this reinforcement can reduce or eliminate undesirable scalloping effects along the upper perimeter of the prosthesis that can otherwise occur when gravity pulls downward on a filled prosthesis.
Implants having fillers of varying density are also known in the art. For example, Inamed's Style 510 Dual Gel breast implant contains two different cohesive gels. The posterior of the implant is made from standard cohesive gel, while the anterior is made from a high cohesive gel. This configuration provides superior projection and support, emphasizing the nipple/areola area of the implant.
Heretofore, fillers of varying density were use only to provide anterior projection. As described herein, cohesive gel fillers of varying density, particularly around the perimeter and in the inferior and posterior regions, may be used to stabilize an implant, maintain its form and reduce or eliminate wrinkling, knuckling, scalloping or other deformation of the shell.